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Guide for Quantitative Approaches to Systemic Safety Analysis (2020)

Chapter: Section 2 - Approaches to Programming Safety Improvement Projects

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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Section 2 - Approaches to Programming Safety Improvement Projects." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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9 Approaches to Programming Safety Improvement Projects Part B of the HSM presents a six-step safety management approach (AASHTO, 2010). While the description in the HSM is specific to the crash prediction procedures included in the HSM, the six-step approach can be generalized to apply to any safety management approach. Many agencies follow these general steps for programming safety improvement projects; the inputs and outputs for each step vary based on the safety management approach employed. Generally, the six-step process helps agencies develop a prioritized list of safety improvement projects (both treatments and implementation locations) and then evaluate the effectiveness of the projects or treatments in reducing crash frequency and/or severity. This generalized six-step process is used here as a framework for comparing differences in roadway safety management methodologies. Three primary roadway safety management methodologies are introduced below and then further described and compared in parts 2.2, 2.3, and 2.4 in this section: • The Crash-History-Based Safety Management Approach is used to program implementa- tion of safety treatments at high-crash locations by analyzing site-specific crash data or using other data-driven processes. • The Systemic Safety Management Approach is used to program implementation of proven safety treatments, primarily low cost, across a large number of sites to reduce crash potential using crash prediction models or rating systems based on roadway features correlated with particular severe crash types. • The Policy-Based Safety Management Approach is used to program implementation of specific treatments or improvements for all similar sites on a road network based on established policies, guidelines, or design criteria. These approaches vary in terms of their intended purpose; the types, quantity, and quality of data required to carry them out; the types of treatments considered for application; and the types of crashes or safety concerns the transportation agency may use them to address. All three approaches are useful, and many agencies use a combination of these approaches to address safety concerns on their systems. The general methodologies of these three safety management approaches are described below, along with their potential advantages and disadvantages. 2.1 Six-Step Approach to Roadway Safety Management Implementing roadway safety management procedures provides useful information for monitoring and reducing crashes on existing highway networks. Traditionally, agencies have implemented a six-step approach to roadway safety management, as described in Part B S E C T I O N 2

10 Guide for Quantitative Approaches to Systemic Safety Analysis of the HSM (AASHTO, 2010). The six steps of the roadway safety management process are as follows: 1. Network Screening—Review a transportation network to identify and rank individual sites based on the potential for reducing crashes. 2. Diagnosis—Evaluate crash data, historic site data, and field conditions to identify crash patterns of interest at each site. 3. Countermeasure Selection—Identify factors that may contribute to crashes at a site and select possible countermeasures to reduce crashes. 4. Economic Appraisal—Calculate the estimated benefits and costs of potential counter- measures and identify individual projects that are cost effective or economically justified. 5. Project Prioritization—Evaluate economically justified improvements at specific sites and across sites to identify a set of improvement projects that meet objectives such as cost, mobility, or environmental impacts. 6. Safety Effectiveness Evaluation—Evaluate the effectiveness of a countermeasure, a combi- nation of countermeasures, or projects implemented at multiple sites in reducing crash frequency and/or severity. These steps are illustrated in Figure 1 and described in more detail below. Network screening is a process for reviewing the transportation network (or portion of the network) to identify and rank sites where improvements, if implemented, have potential to reduce the number or severity of crashes. The primary steps in network screening are as follows. Step 1. Establish Focus. Identify the purpose or intended outcome of the network screen- ing analysis. The screening may be to find locations with the highest crash frequencies, the highest crash rates, the most severe crashes, or the largest concentration of specific crash types. Step 2. Identify Network and Establish Reference Populations. Specify the type of sites or facilities being screened (i.e., segments, intersections, ramps) and identify groupings of Figure 1. Six-step roadway safety management process (adapted from AASHTO, 2010).

Approaches to Programming Safety Improvement Projects 11 similar sites or facilities. Prioritization of individual sites is made within a reference population. Step 3. Select Performance Measures. Select the performance measure or measures that will be used to evaluate the potential to reduce the number of crashes or crash severity at a site. Examples of performance measures include historical crash counts or rates, predicted or expected crash frequencies, and the count or presence of identified contributing factors. Key considerations in selecting a performance measure include data availability, regression- to-the-mean bias, and how the performance threshold is established. Step 4. Select Screening Method. Select the screening method consistent with the performance measure(s) selected. Typically, roadway segments are screened using either a sliding window or peak searching approach, while intersections, ramp terminals, and ramps are screened using a ranking method that analyzes the entire site as a whole. Traffic data management systems may be used to automate the screening process. Step 5. Screen and Evaluate Results. Conduct the screening analysis. The result will be a list of sites prioritized according to the selected performance measure(s). Sites higher on the list are considered most likely to benefit from implementation of safety countermeasures. If multiple performance measures are used for network screenings, sites that repeatedly appear at the higher end of the lists should become the focus of further site investigations, while those sites consistently on the lower end of the lists could be ruled out for further investigations. Further study of the high-priority sites will yield the type of safety improve- ments most likely to be cost effective. Diagnosis is performed on a site-by-site basis to identify the causes of crashes and discover potential safety concerns or crash patterns before potential countermeasures are selected. The general steps of the diagnostic process include: Step 1. Safety Data Review. Review crash locations, types, severities, and environmental con- ditions to identify potential patterns in the crashes. Reviewing multiple years of crash data improves the reliability of the review. Step 2. Assess Supporting Documentation. Review previous studies and documentation covering the site vicinity to identify known issues, opportunities, and constraints. Types of supporting documentation that may be helpful to assess safety issues at individual sites include traffic volumes for all modes, as-built construction plans, relevant design criteria and guidelines, inventory of field conditions, results of previous speed studies, road safety audit findings, photos and/or video logs, maintenance logs, etc. Step 3. Assess Field Conditions. Conduct a site visit to observe how different modes travel to and through the site. Visiting the site during different times of day and under different lighting and weather conditions may provide insight to safety concerns. Elements to consider during the assessment may include roadway and roadside characteristics, traffic conditions, traveler behavior, land use, weather conditions, and evidence of previous crashes. Following the safety data review and assessment of supporting documentation and field conditions, relevant information can be compiled to identify specific crash patterns to be addressed by safety countermeasures. During countermeasure selection, sites are further evaluated to identify factors that may contribute to particular crash types or safety concerns. For each crash pattern of interest, multiple contributing factors may be identified. A useful framework for identifying contributing factors is to consider conditions before, during, and after a crash and human factors, vehicle, and roadway elements. Checklists and resources, such as the HSM, the NCHRP Report 500 series, and the Contributing Factors for Focus Crash Types and Facility Types: Quick Reference Guide

12 Guide for Quantitative Approaches to Systemic Safety Analysis (Porter et al., forthcoming), provide examples of contributing factors associated with a variety of crash types. Having identified possible contributing factors, the next step is to identify countermeasures that may address the contributing factors. This requires engineering judgment and knowledge of resources that document the known safety effectiveness of treatments based on previous research. The HSM and the CMF Clearinghouse are two resources that provide quantitative CMFs for countermeasures. Knowledge of the safety effectiveness estimates of treatments and conditions for their application help practitioners select preferred treatments for further economic analysis. Economic appraisal is performed to compare the benefits of potential safety improvements to the costs of implementing the improvements. Two main types of economic appraisals are benefit-cost and cost-effectiveness analyses. For a benefit-cost analysis, the benefits of the treat- ment (i.e., the number of crashes the countermeasure is expected to prevent) are estimated and translated into monetary value and then are compared to the countermeasure’s implementa- tion cost by calculating the ratio of the benefits to the costs. For a cost-effectiveness analysis, implementation costs are compared to the estimated number of crashes expected to be reduced due to implementation of a countermeasure to estimate the dollars spent to reduce a single crash. As an outcome of the economic appraisal process, the countermeasures considered for possible implementation at a given site can be prioritized based on: • Benefit-cost ratio (i.e., number of crashes reduced expressed in monetary terms divided by construction cost). • Cost-effectiveness index (i.e., expressed as dollars spent per crash reduced). • Safety benefits (i.e., number of crashes reduced expressed in monetary terms). • Net benefits (i.e., number of crashes reduced expressed in monetary terms minus the construction cost). • Number of crashes reduced by severity (e.g., total, fatal and serious injury, and/or fatal and injury). • Construction cost. During project prioritization, each countermeasure determined to be economically justified for a specific site during economic appraisal is then considered for project programming and implementation. During this step, project alternatives are reviewed and ranked. The simplest method for prioritizing safety improvement projects is ranking them by economic effectiveness measures such as those listed above. Other optimization approaches consider the impact of budget constraints in developing an optimized set of improvement projects. Other factors such as timing with upcoming projects, environmental impacts, and public acceptance also influence decision making during project prioritization. Safety effectiveness evaluation is the final step of the roadway safety management process. This step develops quantitative estimates of how a treatment, project, or groups of projects affect crash frequencies or severities. Estimating the overall safety effectiveness of a treatment or group of projects informs future safety decision making and policy development. Different types of performance measures can be used to quantify the safety effectiveness of a treatment or group of projects, including measures such as a percentage reduction in crashes, a shift in the proportion of crashes by collision type or severity level, or a comparison of the safety benefits to the cost of the treatment/project. When distinguishing between the crash-history-based safety management approach, the systemic safety management approach, and the policy-based safety management approach, the primary differences are related to the network screening, diagnosis, and countermeasure selection steps. It is these first few steps in the six-step roadway safety management process where the primary differences in the purpose and conceptual approach to roadway safety management lie. The next three sections highlight these differences.

Approaches to Programming Safety Improvement Projects 13 2.2 Crash-History-Based Safety Management Approach The purpose of the crash-history-based safety management approach, sometimes referred to as a “black-spot” or hot-spot analysis, is to identify locations on the system where a high frequency or rate of crashes has occurred and to improve those sites to remedy the situation. Implementing the crash-history-based safety management approach requires high-quality crash data with accurate location data throughout the roadway network. Agencies typically utilize the six-step roadway safety management process as described above when implementing a crash-history-based safety management approach. The primary factors that distinguish the crash-history-based safety management approach from the systemic and policy-based safety management approaches are conceptual approaches to network screening and diagnosis and countermeasure selection. With the crash-history-based safety management approach, sites are ranked for potential safety improvement based on their overall crash experience (i.e., all crash types combined). Crash experience may be estimated based on traditional performance measures—such as observed crash frequencies, observed crash rates, or equivalent property damage only (EPDO) observed crash frequencies—or other performances measures considered more statistically reliable as described in the HSM—such as level of service of safety (LOSS) or expected and excess crash frequencies that make use of crash prediction models or SPFs. For each performance measure, the site-specific information or data are used to estimate the overall crash experience at a site. Sites with higher crash experience based on the selected performance measure are considered to have higher potential for safety improvements, while sites with lower crash experience are considered to have less potential for safety improvement. With the crash-history-based safety management approach, the goal is to reduce crash patterns of interest that occur with a high frequency at individual locations and to do so at sites with the highest overall crash experience. In most cases, it does not matter that at one site rear-end crashes occur with high frequency, at another site angle crashes occur with high frequency, and at another site head-on crashes occur with high frequency. It simply matters that whatever performance measure is used, sites with higher overall crash experience are given a higher priority of potential safety improvement compared to sites with lower overall crash experience. In some cases, though, the crash-history-based safety management approach is also used to identify sites with a high frequency of target crashes. With most performance measures, the crash-history-based safety management approach is considered reactive in nature, as individual sites are identified for potential safety improvement only after having a documented crash history substantial enough to make them rank higher than other sites on the prioritized list. Sites that rise to the top of the priority list for potential safety improvement tend to be located on urban corridors and at urban intersections where traffic volumes are highest. This can lead to a disproportionally low safety investment in rural loca- tions where crashes tend to be more dispersed around the network. After the network screening step identifies priority locations based on overall crash experience, the diagnostic process is performed on a site-by-site basis. Crash data are reviewed at individual sites to identify trends in crash patterns and types of crashes to be remedied at each location. Some sites may have a documented history of rear-end crashes, while other sites may have a history of angle crashes or head-on crashes. The type of crashes that occur with high frequency at an individual site may not be particularly important during network screening as treatments are tailored to remedy the crash patterns of interest at the individual locations. In many cases, a full range of infrastructure treatments, from low to high cost, is considered for potential implementation to address different crash types. Consequently, the diagnosis and counter- measure selection process for the crash-history-based safety management approach is typically much more involved and time consuming than for the other safety management approaches.

14 Guide for Quantitative Approaches to Systemic Safety Analysis Economic analyses are then performed at the site level, considering the potential counter- measures identified in the previous step. The costs of recommended countermeasures for the site are compared to the potential economic savings due to crashes prevented by the countermeasures. Results of the economic analysis can be used to prioritize sites for safety investment in such a way that the agency can expect the highest possible benefit from its avail- able safety budget. With the crash-history-based analysis approach, a safety effectiveness evaluation is usually performed using a simple before-after analysis approach to compare the number of crashes before improvement (for X number of years) to the number of crashes that occur after imple- mentation of the countermeasure (for X number of years). The difference between these two values indicates the effect of the countermeasure on safety performance. A safety effectiveness evaluation may also be performed using other approaches such as a before-after study with comparison group or traffic volume correction to address some of the limitations of the simple, before-after analysis approach, or an empirical Bayes (EB) before-after study approach. The benefits of a crash-history-based safety management approach include the ability to: • Focus funds where there is a documented crash history. • Identify treatments that address the specific crash patterns at each site. • Tailor treatments to the specific characteristics of the locations. • Address a wide range of safety conditions and tradeoffs using a quantitative and logical process. Potential limitations or disadvantages associated with the crash-history-based safety manage- ment approach include: • Crashes must occur at a site before an improvement is made. • Safety improvements may be made at sites to remedy specific crash types that may not occur again, even if no improvements are made. • Implementation of higher-cost safety improvements at a limited number of sites may not effectively reduce crash frequency across the network (Gross et al., 2016). • Crash types that occur frequently but are dispersed across the network may not be effectively addressed (Gross et al., 2016). 2.3 Systemic Safety Management Approach The purpose of the systemic safety management approach is to be more proactive in program- ming safety improvements and to address specific crash types not well suited for remedy using a crash-history-based safety management approach by widely implementing primarily low-cost countermeasures. The systemic safety management approach uses safety performance measures related to expected future crashes (such as expected crash frequencies or the presence of crash contributing factors) for network screening and project site prioritization. Crash types that occur with high frequency across the roadway network but not concentrated at individual locations (i.e., crash types that occur with high frequency but are highly dispersed across a roadway network), tend to be overlooked when ranking sites using a crash-history- based safety management approach. The systemic safety management approach can be used to address such crash types by treating many sites that have potential for experiencing that type of crash with low-cost treatments. In many cases, these widely dispersed crash types are consistent with target crashes identified in an agency’s strategic highway safety plan (SHSP). Some of the specific crash types that agencies have focused on when implementing systemic safety management procedures include:

Approaches to Programming Safety Improvement Projects 15 • Lane departure, • Rollover, • Fixed object, • Speed-related, • Younger driver involvement, • Impaired driving, • Pedestrians, • Bicyclists, and • Nighttime. One option for an agency to identify target crash types to address using a systemic safety management approach is to refer to a state or regional SHSP that documents emphasis areas or target crash types for the state’s or region’s safety program. Referring to a state or regional SHSP to identify focus crash types for systemic safety analysis does not require the use of any specific type of data (i.e., crash or roadway inventory); however, unless the SHSP specifically states that a target crash type is to be addressed through systemic safety management, it may not be readily apparent which target crash types within an SHSP should be addressed through systemic safety management. An agency may have to infer or deduce which target crash types within the SHSP should be addressed through systemic safety. Referring back to the general six-step roadway safety management process, the network screening step in a systemic safety management approach generally uses one of two methods to prioritize sites for potential safety improvement. With one method, crash prediction models or SPFs are used to calculate predicted and/or expected crash frequencies of target crash types at specific sites. Predicted crash frequencies are estimated directly from the SPFs, while expected crash frequencies are calculated using statistical procedures to combine observed crash frequen- cies and predicted crash frequencies from SPFs. With the publication of the HSM and recent emphasis on the use of SPFs for roadway safety management, many agencies have developed their own SPFs or calibrated existing SPFs using their own crash and inventory data. The development of agency-specific SPFs has allowed agencies to implement systemic safety manage- ment approaches within their HSIP. With systemic safety and the use of SPFs, the emphasis is on calculating predicted, expected, or excess crash frequencies for target crash types. With the second network screening method, a rating system is developed to represent crash potential at sites within the network. Crash potential is generally assessed by identifying crash contributing factors present at each site. Crash contributing factors may be identified based on published research or through a quantitative analysis of site characteristic data to determine which characteristics are overrepresented at sites where certain crash types occur. Sites identi- fied as having the highest crash potential are given the highest priority for programming safety improvements. Low-cost countermeasures proven to effectively reduce crashes are generally the first treat- ment types considered for implementation as part of a systemic safety management approach (although higher-cost countermeasures can be considered as well). Through the use of low-cost safety improvements, more sites can be improved, which can lead to a greater reduction in target crashes across the network. Types of countermeasures that agencies have implemented as part of their systemic safety management projects include: • Roadway segments: – Rumble strips (both shoulder and centerline), – Cable median barrier, – SafetyEdge, – High friction surface treatments, – Enhanced pavement markings,

16 Guide for Quantitative Approaches to Systemic Safety Analysis – Curve warning signs, – Chevrons/delineators, – Lane/shoulder widening, – Speed feedback signs, – Tree/clear zone removal. • Intersections: – Signal backplates, – Crosswalk enhancements—striping, signing, rectangular rapid flashing beacons, – Countdown pedestrian signals, – Pedestrian refuge islands, – Curb extensions, – Reflective strips on sign posts, – Mini-roundabouts, – Lighting. Countermeasures are chosen to remedy target crash types and address the crash contributing factors identified for the specific crash types of interest and are then implemented at many sites where those crash contributing factors are present, regardless of previous crash history. Typically, one or more proven, low-cost countermeasures are initially identified for consider- ation to address a particular target crash type. With the systemic safety management approach, much of the diagnosis and countermeasure selection process is performed ahead of time in terms of identifying crash patterns of interest and potential countermeasures. Consequently, in relation to the six-step safety management approach, the diagnosis and countermeasure selection process involves less effort and is less time consuming for the systemic safety management approach than it is for the crash-history- based safety management approach. In a systemic safety management approach, the economic evaluation is typically based on the expected number of crashes reduced due to implementation of the systemic countermeasure(s) and the overall project costs. However, since specific countermeasures have already been identi- fied for implementation and a prioritized list of implementation locations has been developed, agencies tend to either determine a specific rating score threshold (for which countermeasures are implemented at all sites that score at or above the threshold) or simply begin countermeasure implementation at the top of the list and work down until funding is exhausted. The expected number of crashes reduced may be estimated using a reliable CMF for the treatment and applying it to the number of crashes experienced in a given time period, over the portion of the system to which the treatment is going to be applied, to justify the expense of the treatment. Generally, in a systemic safety management approach, the countermeasures chosen for implementation already have a well-documented and reliable estimate of safety effectiveness. Therefore, a safety effectiveness evaluation is not always important to the agency, but further evaluation is also useful to inform future decision making. Therefore, agencies may have interest in evaluating the success of their systemic treatment applications. Quantitative impacts of systemic treatment applications are most commonly analyzed using a trend analysis, a simple before-after study method, an EB before-after study method, or a shift of proportions method. However, the methodological approach to evaluation depends on the type and amount of data available, the goals of the evaluation, and the agency resources available to complete the evaluation. The potential benefits of implementing a systemic safety management approach include the following: • This approach can be used in the absence of high-quality, historical, site-level crash data (Gross et al., 2016).

Approaches to Programming Safety Improvement Projects 17 • This approach is proactive because countermeasures can be programmed for implemen- tation at locations that may not have a history of crashes (Gross et al., 2016). In particular, even sites with zero crash history can be identified for potential safety improvement using a systemic safety management approach. • The approach helps agencies broaden their traffic safety efforts and consider the potential for future crashes as well as crash history when identifying where to make safety improvements (Preston et al., 2013). • This approach provides the ability to program projects further into the future as projects can be based on the presence or absence of crash contributing factors (i.e., roadway charac- teristics) that do not change frequently from year to year. • With this approach, it may be easier to more equally distribute safety funds regionally or across jurisdictions compared to programming safety improvements based solely on a crash- history-based safety management approach. • This approach is adaptable based on available data. The potential limitations or disadvantages associated with the systemic safety management approach include: • Available software that can be used for quantitative systemic safety analyses is used on a limited basis either because it is considered expensive, data intensive, or agencies do not invest the time and resources to collect the necessary data for use with the software. • Project prioritization and the process for evaluating the benefits of a systemic safety manage- ment approach (i.e., project evaluation) are not well understood because of the lack of before crashes at improvement sites. • Staff may be reluctant to implement a systemic safety management approach because it deviates from the traditional crash-history-based safety management approach (i.e., hot- spot analysis). • Agencies have little guidance on how to allocate funding to support programming safety improvements identified through a combination of crash-history-based and systemic safety management approaches. 2.4 Policy-Based Safety Management Approach The purpose of the policy-based safety management approach is to bring design or opera- tional features of sites up to a specified standard or policy. The policy-based safety management approach is intended to reduce both liability and crash potential. The countermeasures imple- mented using this safety management approach are often those proven to effectively reduce crashes. After a countermeasure has been shown to effectively reduce crashes, agencies may develop a policy to implement the countermeasure as part of their regular design, construction, operations, and maintenance programs, including new construction and reconstruction. The agency may also choose to improve existing facilities for safety purposes only (Gross et al., 2016). A policy-based safety management approach promotes the application of low-cost counter- measures proven to effectively reduce crashes. Examples of countermeasures installed as part of a policy-based safety management program include: • Installation of retroreflective backplates on all new signal installations and signal upgrades. • Installation of shoulder rumble strips/stripes on all two-lane roads with a shoulder of sufficient width. • Installation of the SafetyEdge treatment for all asphalt paving projects without curbs. In a policy-based safety management approach, detailed economic analyses are generally not performed. Once the policy for treatment implementation has been determined, the agency

18 Guide for Quantitative Approaches to Systemic Safety Analysis budgets the necessary funding into future projects as part of construction and/or maintenance costs. Expected benefits may be estimated using a reliable CMF for the treatment and applying it to the number of crashes experienced in a given time period over the portion of the system to which the treatment is going to be applied. This approach provides general systemwide estimates of crash reductions that can be used to justify the expense of the treatment. If a safety effectiveness evaluation is performed, it is generally conducted over many similar sites within the network. Often, a before-after analysis will be conducted for all or a large number of the sites where the treatment was implemented. Alternatively, an agency may choose to evaluate how effective its systemwide implementation of a treatment was by considering the change in crash frequency or rate for a targeted crash type over the entire system after treat- ment implementation. The potential benefits of implementing a policy-based safety management approach include the following: • Countermeasures proven to effectively reduce crashes are implemented. • This approach can be used in the absence of high-quality, historical, site-level crash data. • This approach is proactive because countermeasures can be programmed for implementation at locations that may not have a history of crashes. • This approach is easily understood. • This approach serves to reduce liability and crash potential. • Safety improvements can be incorporated into different types of projects (e.g., new construc- tion, reconstruction, rehabilitation, and maintenance). • Implementation costs may go down when installation is programmed into scheduled construction and maintenance projects, eliminating separate project start-up and traffic control costs. The potential limitations or disadvantages associated with the policy-based safety management approach include the following: • It may take years to bring the targeted facility types up to the desired standard/policy. • This approach can be perceived as increasing the total cost of projects by adding counter- measure implementation costs that may not have otherwise been included. • Resources may not be allocated as efficiently as possible because treatments may be imple- mented at locations with low potential to reduce crashes. 2.5 Summary Many agencies follow a six-step approach to programming their safety improvement projects: network screening, diagnosis, countermeasure selection, economic appraisal, project prioritiza- tion, and safety effectiveness evaluation. Within this general six-step process, agencies typically follow three variations of roadway safety management approaches: • Crash-history-based safety management. • Systemic safety management. • Policy-based safety management. These roadway safety management approaches vary in terms of the types, quantity, and quality of data required to carry them out; the types of treatments considered for application; and the types of crashes or safety concerns the transportation agencies may address. The systemic safety management approach provides flexibility, is adaptable based on available data, and to some extent, is a hybrid of the crash-history-based and policy-based safety management approaches. Like the crash-history-based safety management approach, the systemic safety

Approaches to Programming Safety Improvement Projects 19 management approach seeks to identify locations where treatments have the highest potential to prevent future crashes to get the most benefit from the safety investment; and like the policy- based safety management approach, the systemic safety management approach focuses on proactively applying lower-cost treatments to many sites to address possible future crashes. The key features that distinguish the systemic safety management approach from the other two approaches are as follows: • Although the crash-history-based safety management approach can address target crashes, in most cases the focus is on initially identifying sites with a high frequency of all crash types and then addressing a range of crash types across the sites to be improved. However, with the systemic safety management approach, only target crash types are addressed and less time and resources are spent on the diagnosis and countermeasure selection steps as some subtasks are no longer necessary or are only cursory in nature due to focusing on particular target crash types and implementation of select countermeasures. • With the systemic safety management approach, low-cost countermeasures are programmed for implementation at a large number of sites of a particular target facility type. However, countermeasures are not programmed for installation at all sites of a particular target facility type as they would be using a policy-based safety management approach (i.e., priorities for programming installation of countermeasures at particular sites of a target facility type are established based on a combination of network screening and economic analysis steps).

Next: Section 3 - Overview of Systemic Safety Management Approaches »
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Traditional approaches to safety have focused on identifying high-crash locations and implementing projects to address predominant concerns at these locations. The systemic approach to safety is a method of safety management that typically involves lower unit cost safety improvements that are widely implemented based on high risk factors.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 955: Guide for Quantitative Approaches to Systemic Safety Analysis provides guidance to state departments of transportation (DOTs) and other transportation agencies on how to apply a systemic safety management approach for identifying safety improvement projects.

Material associated with the report includes NCHRP Web-Only Document 285: Developing a Guide for Quantitative Approaches to Systemic Safety Analysis and a PowerPoint of the summary of project findings and future research needs.

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